Abstract:

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NIL(Nano Imprint Lithography) is one of the most promising lithography techniques.
There are many variants of NIL, and two major techniques of them are thermal NIL and UV NIL.
Here, we focus ourselves on the thermal NIL. During the thermal NIL, the polymeric patterns
experience large mechanical strain and high temperature, and this often leads to malformation of
polymeric patterns. So it is needed to improve the pattern fidelity and contrast, and these are believed
to be closely related to the process condition and mechanical properties. In thermal NIL, PMMA is
widely used and chosen as target polymer. Generally, mechanical properties in nano scale are really
hard to acquire.
In this study, we estimate the mechanical properties of PMMA by molecular dynamic simulation.
These properties will be used as input of continuum simulation. We will estimate stress-strain
relationship of PMMA. This stress-strain relationship depends on strain rate and temperature. So we
will study about strain rate and temperature effect.

Abstract: Equal Channel Angular Extrusion (ECAE) has become a very popular tool for studying the evolution of microstructure and properties under severe plastic deformation. It is believed that the stress-strain characteristics are uniform in a cross-section of the billet and this uniformity of the stress-strain distribution ensures the uniformity of microstructure and mechanical properties in ECAE processed billet. However, some experimental data such as the fracture of the extruded billet, which is initiated at the inner surface of the sample, has caused doubts about uniformity of stress-strain distribution. This non-uniformity has been proved recently by Finite Element Simulation.
In this paper the studies of the positive role of the applied back-pressure during ECAE are reviewed and the influence of a back-pressure on the uniformity of the stress-strain distribution, strain localisation, die corner filing, and the prevention of fracture is shown. The effect of back-pressure on grain refinement and improvement in mechanical properties is emphasized. The paper summarises our results from over seven years of work using a unique machine for ECAE with computer-controlled back-pressure and velocity of the backward punch.

Abstract: Thermal residual stress in diamond film deposited onto Mo substrate was simulated and analyzed comprehensively by using the finite element method on condition that the substrate’s plasticity was considered. The contour plots of the stresses were described. Moreover, the effect of the film’s thickness on thermal residual stress was investigated. The results show that every stress component in the film has the remarkable stress concentration at the intersection of the interface and the side of the film. The location of maximum tensile principal stress in the film is at the upward face or side face of the film or the interface. The magnitude of maximum tensile principal stress increases when the film becomes thicker. These conclusions are useful to the proper choice of the film’s thickness and the effective control of the stresses during preparation of diamond film.

Abstract: In recent years, tube hydroforming has been applied in automobile and airplane industries, to decrease weight. In general, the determination of internal pressure path is a key factor in improving the formability in tube hydroforming. One of the effective methods in improving the tube hydroforming is using the pulsating internal pressure path. In this research, hydroforming of bi-layered tubes under pulsating pressure in x-shaped die is simulated by means of three dimensional finite element method. Some numerical results were compared with experimental results and show good correlation. Influence of pulsating pressure on the thickness and stress distribution have been also studied. It was shown that pulsating pressure improves the formability in hydroforming of bi-layered tubes via continues and gradual removing returnable wrinkling which is caused by a low pressure in this process. In addition, effect of some key parameters such as friction and die corner filling have been investigated.

Abstract: The application of ABAQUS finite element software non-linear finite element analysis of brick masonry walls with structural column. Build three brick masonry wall models, and analysis of the damage form of the wall under different vertical compressive stress and horizontal force. Thus the analysis result compared with the calculation result of the relevant specification formula, in order to get validate compression influence of masonry aseismic walls. It turned out that different vertical compressive stress effect the shear capacity, and failure mode of brick masonry wall structure with a structural column.

Abstract: Many engineering specifications, manufacturing procedures, inspection and quality control have begun to require that the residual stress of a particular component be evaluated. This is becoming as commonplace as the demands on the mechanical properties. In the country there are few research laboratories qualified to perform these tests and also found a worrying lack of skilled labor. Studying the formation and distribution of residual stress fields will improve the operational criteria of wheel safety, among other gains. It is known that these residual stress fields could be added to the effects of system load (tare weight plus occupation of vehicle traction, braking and torque combined). The results obtained used drilling method and rosette type strain gages, are convergent with similarity to those obtained using FEA simulation over critical region for global and superficial in principal stresses mode. The relevance of the present study and research on residual stresses meets safety improvements in cars wheel industry.